1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method for flattening a semiconductor substrate or other object to be polished by chemical mechanical polishing.
2. Description of the Related Art
In the process of production of a semiconductor device, for example, a polishing apparatus using chemical mechanical polishing is used for flattening the uneven surface resulting from the multilayer structure of the semiconductor device. An example of this polishing apparatus is shown in FIG. 1 and FIG. 2.
A polishing apparatus 101 shown in FIG. 1 and FIG. 2 is provided with a polishing plate 121 which is rotatably held by a shaft 122 and to a front surface of which a polishing pad 111 is bonded, a polishing head 103 which is rotatably held by a shaft 103 arranged facing the polishing pad 111, and a slurry feed nozzle 131 for feeding a mixture 141 of a polishing agent (slurry) made of a mixture of for example potassium hydroxide (KOH) and silicon dioxide (SiO.sub.2) and pure water onto the polishing pad 111.
A polishing head 102 of the polishing apparatus 101, as shown in FIG. 2, is formed with a recessed holder 102a for holding a wafer W. The wafer W is held at this holder 102a via for example a backing film for holding the wafer W at the holder 102a.
The polishing apparatus 101 feeds the mixture 141 of the slurry and the pure water from the slurry feed nozzle 131 onto a center portion of the polishing pad 111 and makes the polishing head 102 and the polishing plate 121 rotate while pressing the wafer W held at the polishing head 102 against the polishing pad 111 with a predetermined pressing force P.
The mixture 141 of the slurry and pure water disperses toward the outer circumference by the rotation of the polishing pad 111 and enters between the polishing pad 111 and the wafer W, whereby the wafer W is flattened by chemical mechanical polishing.
However, in the polishing apparatus 101 having the above configuration, in order to interpose a sufficient amount of slurry between the polishing pad 111 and the wafer W, it is necessary to continuously feed the slurry from the slurry feed nozzle 131, so the amount of consumption of the slurry is increased.
The cost of the slurry is relatively high, so if the amount of consumption of the slurry is increased, there is the disadvantage that the running cost (COO: cost of ownership) of the polishing apparatus 101 is increased.
On the other hand, since the slurry is a mixture of potassium hydroxide (KOH) and silicon dioxide (SiO.sub.2), it naturally easily forms hydrogen bonds--resulting in an increase in the particle size of the slurry.
The slurry having the increased particle size is apt to cause polishing scratches (microscratches and macroscratches) on the wafer W during polishing, therefore there was the disadvantage that the percentage of defective wafers W increased and the yield was lowered.